The research aims to attain a more complete understanding of mitosis in order to find ways to specifically arrest cells in mitosis. Human, hamster and human-hamster hybrid cells are used as the main source of experimental material. Cell culture, genetic, cytological, ultrastructural, and biochemical methods will be used in the experiments. A series of temperature-sensitive mutant hamster cell lines in which mitosis is defective at the nonpermissive temperature has been isolated. Biochemical and ultrastructural analyses of the mutants will be conducted to determine the specific gene products involved in the mutations as a means to define molecular species required for mitotic progression. The mutants will be utilized for elucidating mechanism of movements of chromosomes and other mitotic structures. Genetic analysis with the mutants will be performed, including the utilization of human-hamster hybrid cells formed between mutant and human cells for localization of mitotic genes on human chromosomes.